1. Field of the Invention
The present invention relates generally to controllers in which X and Y outputs are produced proportional to X and Y inputs. More particularly the present invention relates to X-Y controllers in which electrical outputs, proportional to X and Y mechanical inputs, are produced, and in which proportionalities are selectively changeable.
2. Description of the Related Art
X-Y controller are used for a variety of purposes, ranging from use with video games to controlling movements of heavy pieces of industrial equipment. In all of these applications, mechanical inputs with respect to X and Y axes are converted into electrical resistances by rotating shafts of first and second potentiometers.
For applications involving the safety of personnel and the safety of expensive equipment, high degrees of reliability and durability are required. In addition, the X-Y controller should be able to withstand rough handling and impacts from foreign objects. For instance, when used for controlling left and right motors of electrically propelled wheelchairs, the controller should be able to withstand the impact of the control handle being driven under a table with no more damage than bending the control handle. However, in prior art designs, such an impact has completely destroyed the X-Y controller.
Typically, in X-Y controllers of prior art configurations, a control handle has been mounted for pivotal movement about the intersection of X and Y axes. First and second rotary potentiometers have been mounted along respective ones of the X and Y axes; and some mechanical mechanism, such as slotted yokes, has been used to translate X and Y movement of the control handle into rotary movement for respective ones of the transducers.
Variations in this typical type of X-Y controller are taught by Hayes, U.S. Pat. No. 4,489,034, issued Dec. 18, 1984; Kim, U.S. Pat. No. 4,587,510, issued May 6, 1986; and Hayes, U.S. Pat. No. 4,620,176, issued Oct. 28, 1986.
When these prior-art type of controllers are used to control a pair of electric propulsion motors, the X-Y controller is rotated 45 degrees about a Z axis. Movement of the control handle away from the operator, that is, in a forward direction between the X and Y axes, provides outputs from both potentiometers that are equal and that are proportional to movement from the intersection of the X and Y axes.
In like manner, movement of the control handle toward the operator, that is, in the reverse direction, provides outputs from both of the potentiometers that are equal, that are proportional to movement from the intersection of the X and Y axes, and that are in the same direction, but that are in the opposite direction from the outputs produced when the control handle is moved in a forward direction.
When the control handle is moved to the right or to the left, the outputs from the potentiometers, while remaining proportional to input of the control handle from the intersection of the X and Y axes, are opposite in direction.
In movements of the control handle forward from the intersection of the X and Y axes, in movements of the control handle rearward, and in movements of the control handle to the left or to the right, the proportionally of output to input is the same.
Thus, when this prior art device is used to control a conveyance such as an electrically-propelled wheelchair, this prior art controller provides the same magnitude of electrical output vs input for reverse propulsion as for forward propulsion. Obviously, this is not desirable, since, for safety, the maximum speed in reverse should be lower than the maximum forward speed.
This equality in proportionality of electrical output to mechanical input is a more serious drawback of this type of X-Y controller when turns are considered.
Typically, an electrically-propelled wheelchair is steered by changing the speed of left and right propulsion motors, as taught in Lautzenhiser et al., U.S. Pat. No. 4,906,906, issued Mar. 6, 1990.
This method of steering provides the capability of making pivot turns. That is, when one wheel rotates in one direction, and the other wheel rotates in the opposite direction at the same velocity, the wheelchair pivots about a substantially stationary axis that intercepts the wheelchair.
However, the ability to make pivot turns, without some method of limiting this maneuver as a function of speed, can make an electrically propelled conveyance extremely dangerous to the operator.
Of additional concern is the fact that, with this prior art type of X-Y controller, the maximum output of the potentiometers doe snot occur when the control handle is moved in the forward direction, nor in the reverse direction, nor at right angles to these directions. Instead, maximum outputs of the potentiometers occur at 45 degrees to any of these directions.
Therefore, when making a turn in which the control handle is moved form an extreme forward position to a position between the extreme forward position and an extreme rightward position, the forward output signal from the left-motor potentiometer is increased by approximately forty-one percent. Unless the wheelchair has already been operating a maximum power, such a maneuver increases the power to the left-wheel motor, causing an overspeeding of the left-wheel motor, and causing a dangerously fast turn.
That is, for a safe turn, the motor rotating the wheel on the outside of a turn should rotate more slowly, in addition to the motor for the inside wheel rotating more slowly. Instead, the prior art controller inherently increases the output signal that controls the outside motor.
This increase in output signal is an inherent function of the fact that the X-Y controller has been rotated 45 degrees about the Z axis to make it more or less suitable for controlling electrically-propelled wheelchairs.
Because of this rotation of 45 degrees about the Z axis, the output from both of the potentiometers, in forward, rearward, right turn, or left turn positions, is equal to their maximum outputs multiplied by the sine of 45 degrees. That is, they produce about 70 percent of the maximum output when the control handle is moved to these positions.
However, since the X-Y controller has been rotated, with respect to the operator, 45 degrees around a Z axis, when the control handle is moved in a direction that is 45 degrees away from directly forward, directly rearward, or directly o one side, it si moved at 0, 90, 180, or 270 degrees with respect to the X-Y controller.
Thus, when the control handle is moved in a direction that is 45 degrees away from forward, one of the potentiometers produces a maximum output and the other potentiometer does not produce any output. This causes the outside wheel of an electrically-propelled wheelchair to overspeed when making turns.
In an attempt to obviate this overpower condition that occurs during turns, a horizontally-disposed plate with a diamond-shaped opening has been used in some prior art designs to prevent movement of the control handle into the areas in which overspeeding occurs during turns.
However, limiting movement of the control handle to this diamond-shaped area has the disadvantage of limiting maximum forward speed to an apex formed by this diamond-shaped path. Therefore, as the conveyance tends to drift to the left or to the right, as caused by slightly unequal loads of the left and right propulsion motors, it has been impossible to move the control handle to the left or to the right to compensate for this drift, without also moving the control handle rearward toward a lower forward speed.
In an attempt to eliminate this drift to one side, and thereby to overcome the control-handle limitations imposed upon the X-Y controller by a diamond-shaped opening, at least one manufacturer has resorted to synchronizing the rotational velocities of the two propulsion wheels. In addition to the original cost and complexity of such an arrangement, maintenance cost have also increased.
In a prior art X-Y controller of common inventorship entity to the present invention, a differential-gear arrangement was used to provide outputs from two potentiometers proportional to input.
In this prior art X-Y controller, the bodies of two potentiometers were mounted onto a framework with the shafts of the potentiometers coaxial and facing each other, and with a bevel gear mounted onto the shaft of each potentiometer. A cage was pivotally mounted onto the potentiometer shafts so that the age could pivot freely about one axis; and a gear shaft was mounted to the cage at right angles to the potentiometer shafts and the two bevel gears. Third and fourth gears where mounted to the gear shaft, and meshed with the first and second gears on opposite side thereof. A control handle was connected to the fourth gear.
When the control handle was moved along one axis, the fourth gear was rotated about the gear shaft, thereby rotating the third and fourth gears in opposite directions, and thereby rotating the first and second gears, together with the potentiometer shafts, in opposite directions.
When the control handle was moved along the other axis, the third and fourth gears along with the cage were rotationally positioned about the other axis, thereby rotating both of the shafts of the potentiometers in the same direction while the gears remained in fixed rotational positions.
The X-Y controller of common inventorship entity and the present invention includes some interesting similarities and differences: Both inventions dispose the transducers coaxially with the shafts thereof proximal to one another, rather than being disposed at 90 degrees, one to the other. However, in this prior design, the transducers are fixedly secured to a base, whereas in the present invention the transducers are pivotally mounted and are pivoted around one axis. Also, in the prior invention, the transducers were connected to the mechanical input by four gears, whereas in the present invention, the shafts are connected directly into the mechanical input device. Further, in the prior design, both X and Y inputs rotate the transducer shafts, whereas in the present invention, an input around the X axis rotates the transducer shafts, and an input around the Y axis rotates the transducer bodies.
However, in spite of these vastly different constructions, the operation is identical in three respects. First: in response to an input around the Y axis, both transducers of both inventions are actuated together, even though, in the prior invention, this function was the result of four gears acting as a differential gear. Second: both transducers produce outputs when a mechanical input is parallel or orthogonal to a transducer axis, whereas in traditional designs, both transducers do not produce outputs, except for mechanical inputs that are not aligned with one of the transducers. Third: the relative rotation of transducer shafts to transducer bodies are in the same direction in response to one, X or Y, input, and are in opposite directions in response to the other input, Y or X.
These similarities are interesting. However, it is evident that it would not be possible to start with these functions of the prior invention and arrive at an invention, such as the present invention, that is so dissimilar in construction.
While this X-Y controller of common inventorship entity was unique, it did not overcome the problem of incurring greater outputs at directions intermediate of the basic forward, reverse, and pivot-turn positions. Also, it had some other limitations which the present invention overcomes. Namely, since the cage was mounted onto the potentiometer shafts, the design had mechanical-strength limitations in that the potentiometers were subject to damage from excessive loads placed onto the control handle. Also, since the control handle also placed loads on the meshing gears, the design had mechanical-strength limitations.
In contrast to the prior art designs, the present invention is extremely resistant to excessive control handle loading, provides different proportionalities between movement along X and Y axes, thereby providing safe and gentle turns when used to control electric wheelchairs, allows changing the proportionality of input to output with respect to movement of the control handle along one axis to compensate for limitations in motor skill of the operator, and allows changing the proportionality with respect to one transducer without changing the proportionality with respect to the other transducer, thereby further allowing compensation for limitations of motor skill of the operator.